With remarkable development of information technology (IT), a great variety of portable information communication devices has been popularized. As a result, in the 21st century, we are moving toward a ubiquitous society in which high-quality information service is possible regardless of time and place.
Lithium secondary batteries are very important to realize such a ubiquitous society. Specifically, lithium secondary batteries, which can be charged and discharged, have been widely used as an energy source for wireless mobile devices. In addition, the lithium secondary batteries have also been used as an energy source for electric vehicles and hybrid electric vehicles, which have been proposed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
As devices, to which the lithium secondary batteries are applicable, are diversified as described above, the lithium secondary batteries have also been diversified such that the lithium secondary batteries can provide outputs and capacities suitable for devices to which the lithium secondary batteries are applied. In addition, there is a strong need to reduce the size and weight of the lithium secondary batteries.
Small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, lightweight battery cells for each device according to the reduction in size and weight of the corresponding products.
The battery cells may be classified into a cylindrical battery cell, a prismatic battery cell, and a pouch-shaped battery cell based on the shapes thereof. Among these battery cells, the pouch-shaped battery cell, which can be stacked with high integration, has a high energy density per weight, and is inexpensive, has attracted considerable attention.
FIGS. 1A and 1B are exploded perspective views typically showing a general structure of a conventional representative pouch-shaped battery cell.
Referring to FIG. 1A, a pouch-shaped battery cell 10 includes an electrode assembly 20 having pluralities of electrode tabs 21 and 22 protruding therefrom, two electrode leads 30 and 31 respectively connected to the electrode tabs 21 and 22, and a battery case 40, in which the electrode assembly 20 is received in a sealed state such that the electrode leads 30 and 31 are partially exposed outward from the battery case 40.
The battery case 40 includes a lower case 42 having a depressed receiving part 41, in which the stacked type electrode assembly 20 is located, and an upper case 43 for covering the lower case 42 such that the electrode assembly 20 is sealed in the battery case 40. The upper case 43 and the lower case 42 are connected to each other by thermal welding in a state in which the electrode assembly 20 is mounted therein to form an upper end sealed part 44, side sealed parts 45 and 46, and a lower end sealed part 47.
As shown in FIG. 1A, the upper case 43 and the lower case 42 may be configured as separate members. As shown in FIG. 1B, on the other hand, one end of the upper case 43 may be integrally formed at a corresponding end of the lower case 42 such that the upper case 43 and the lower case 42 may be hingedly connected to each other.
In addition, as shown in FIGS. 1A and 1B, the pouch-shaped battery cell is configured to have a structure in which electrode terminals constituted by the electrode tabs and the electrode leads connected to the electrode tabs are formed at one end of the electrode assembly. Alternatively, a pouch-shaped battery cell configured to have a structure in which electrode terminals are formed at one end and the other end of an electrode assembly may also be manufactured using the above-described method.
Meanwhile, FIGS. 1A and 1B show the stacked type electrode assembly. Alternatively, the pouch-shaped secondary battery of FIGS. 1A and 1B may be manufactured using a jelly-roll type (wound type) electrode assembly configured to have a structure in which a long sheet type positive electrode and a long sheet type negative electrode are wound in a state in which a long sheet type separator is disposed between the positive electrode and the negative electrode or a stacked and folded type electrode assembly configured to have a structure in which a plurality of stacked type electrode assemblies is folded using a continuous separation film having a long length.
In general, a protection circuit module (PCM) that is capable of effectively controlling an abnormal state, such as overcharge or overcurrent, of the lithium secondary battery is mounted in the lithium secondary battery in a state in which the PCM is connected to a battery cell of the lithium secondary battery.
FIG. 1C is an exploded perspective view typically showing a conventional battery pack configured to have a structure in which a PCM is mounted at a pouch-shaped battery cell.
Referring to FIG. 1C, a battery pack 50 includes a pouch-shaped battery cell 10 having electrode terminals 30 and 31 protruding therefrom and a PCM 60 mounted at the pouch-shaped battery cell 10 in a state in which the PCM 60 is connected to the electrode terminals 30 and 31, external input and output terminals 61 being exposed from the PCM 60.